Medical endoprosthesis or implants for a wide variety of applications are known from the state of the art in great diversity. Implants as defined by the present invention are notably endovascular prostheses, such as stents.
Stents are used in treatments frequently employed today, in particularly in the case of cardiovascular diseases. The stents are used to keep hollow organs clear. They frequently have a body in the shape of an optionally perforated tubular or hollow-cylindrical mesh structure, which is open at both longitudinal ends. The tubular base mesh of such an endoprosthesis is inserted into the hollow organ requiring treatment and supports the hollow organ treated there. Stents have become established in particular for the treatment of blood vessel diseases. Narrowed areas in blood vessels can be expanded and kept open when using stents, optionally adding a balloon catheter, for example, resulting in increased lumen. For example when treating cancer, stents may also be used to keep narrowed air passages (such as the windpipe), bile ducts or the esophagus, which are caused by malignant tumors, open after dilation.
While through the use of stents or other implants, an optimal cross-section of the hollow organ can be achieved, which is primarily necessary for successful treatment, the lasting presence of such a foreign object triggers a cascade of microbiological processes, which favor the inflammation of the hollow organ to be treated or necrotic changes, for example, and due to the formation of plaque may result in gradual blockage of the stent. In the worst case, this change of the hollow organ may cause an occlusion of the hollow organ.
It is desirable to largely avoid the aforementioned inflammation-favoring effect of implants in the future, because this reduces the effectiveness of the implant and may cause further damage to the treated organism.
So-called drug-eluting stents (DES), which release small quantities of pharmaceutical agents such as sirolimus and paclitaxel, are already being used to inhibit the formation of new cells. Such DES are employed in particular for the treatment of coronary heart disease—notably at an increased risk of restenosis (for example in diabetic patients).
Furthermore, it has been shown that abluminally coated DES are conceptually superior to completely coated DES, because they exhibit improved ingrowth behavior. The abluminal layer contains the pharmaceutically active substance, for example sirolimus and paclitaxel. However, tests of abluminally coated stents showed that the layer adhesion of the abluminal layer is poor and may result in regulatory, production-related and possibly even clinical problems.
In order to improve the adhesion of the layer, so far the material parylene has been tested as an adhesion promoter; in addition, plasma treatment has been tested. These methods, however, did not result in any significant improvement in the adhesion of the abluminal coating.
The document U.S. 2008/0206440 A1 describes a bioabsorbable stent comprising struts, each of which contains, abluminally, a pharmaceutical composition, which is encapsulated by a coating, the matrix of which includes antibodies. The antibodies, or antibody fragments, contained in the antibody coating are used to bind antigens of the hollow organ, which are specific to the treated individual. In this way, the ingrowth behavior of the stent into the respective vascular cells is supported.
Document U.S. 2008/0097575 A1 describes a medical device comprising a coating. The coating is designed so that a luminal surface, or a surface coming in contact with blood, is provided for a stent or a stent graft and that, additionally, an outer surface is implemented, which is adjusted to improve the contact between the adjoining tissue and the stent or stent graft. This design of a stent or stent graft does not contain a solution according to which better adhesion of the abluminal layer can be achieved.